UV curable coatings have been, in the main, composed of three (3) components--(1) a UV activated catalyst, (2) an unsaturated polyester of a multi-functional acrylate or acrylate oligomer and, (3) a low viscosity monomer such as styrene, an acrylate, methacrylate, vinyl pyrrolidone, or vinyl caprolactone, etc. A newer type of UV curable coating replace group three (3) by solvents which are removed prior to UV curing.
It would be desirable to avoid the toxicity problem of the third component of the coating while avoiding and also the need for solvent removal.
Multi-functional, non-oxygen inhibited polyacrylates, such as dipentaerythritol hydroxy pentacrylate are a well known group of UV curable monomers. These are however too viscous to be readily used in many coating procedures where thin coatings (final after-cure thickness) of between 3 to 4 microns, up to about 250 microns (1 mil) are required. Traditionally, as stated above, this problem had been overcome by using vinyl monomers or heat dried solvents. Many of the previously used solvent/diluents have the disadvantage of being environmentally hazardous. This manifests itself either in the formation of hazardous vapor during the curing step when the solvent is driven off or else the solvent/monomer mixture gives off undesirable vapors or is a skin irritant against which protective clothing would be required. Unfortunately however, in many locations where these materials are used, ventilation is either inadequate or the proper protective clothing is not used. It would therefore be desirable to find a solvent system which would avoid either or both of these problems.